This invention relates to a method and apparatus for correcting a printhead, a printhead corrected by this apparatus, and a printer using this printhead. More particularly, the invention relates to a method and apparatus for correcting, by way of example, a full-line printhead equipped with a plurality of print elements corresponding to the printing width of a recording medium, a printhead corrected by this apparatus, and a printer using this printhead.
A printer or the printing section of a copying machine or facsimile machine is so adapted as to print an image, which comprises a dot pattern, on a recording medium such as a paper, a thin plastic sheet or fabric based upon image information.
Among these printing apparatuses, those which are the focus of attention because of their low cost are mounted with printheads that rely upon the ink-jet method, the thermosensitive-transfer method or the LED method, etc., in which a plurality of printing elements corresponding to dots are arrayed on a base.
In a printhead in which these printing elements are arrayed to correspond to a certain printing width, the printing elements can be formed through a process similar to a semiconductor manufacturing process. Accordingly, a transition is now being made from a configuration in which the printhead and driving integrated circuitry are arranged separately of each other to an integrated assembled configuration in which the driving integrated circuitry is structurally integrated within the same base on which the printing elements are arrayed. As a result, complicated circuitry involved in driving the printhead can be avoided and the printing apparatus can be reduced in size and cost.
Among these types of printing methods, the ink-jet printing method is particularly advantageous. Specifically, according to this method, thermal energy is made to act upon ink and the ink is discharged by utilizing the pressure produced by thermal expansion. This method is advantageous in that the response to a printing signal is good and it is easy to group the orifices close together at a high density. There are greater expectations for this method in comparison with the other methods.
When the printhead is manufactured by applying a semiconductor manufacturing process and, in particular, when numerous printing elements that are to be made to correspond to the printing width are arrayed over the entire area of a base, it is very difficult to manufacture all of the printing elements without any defects. As a consequence, the manufacturing yield of the process for manufacturing the printhead is poor and this is accompanied by higher cost. There are occasions where such a printhead cannot be put into practical use because of the costs involved.
Accordingly, methods of obtaining a full-line printhead have been disclosed in the specifications of Japanese Patent Application Laid-Open (KOKAI) Nos. 55-132253, 2-2009, 4-229278, 4-232749 and 5-24192 and in the specification of U.S. Pat. No. 5,016,023. According to these methods, a number of high-yield printheads each having an array of printing elements of a comparatively small number of orifices, e.g., 32, 48, 64 or 128 printing elements, are placed upon (or upon/below) a single base at a high precision in conformity with the density of the array of printing elements, thereby providing a full-line printhead whose length corresponds to the necessary printing width.
It has recently become possible on the basis of this technique to simply manufacture a full-line printhead by arraying printing elements of a comparatively small number (e.g., 64 or 128) of orifices on bases (also referred to as "printing units") and bonding these printing units in a row on a base plate in highly precise fashion over a length corresponding to the necessary printing width.
Though it has thus become easy to manufacture a full-line printhead, certain performance-related problems remain with regard to a printhead manufactured by the foregoing manufacturing method. For example, a decline in printing quality, such as density unevenness, cannot be avoided. The cause is a variation in performance from one printing unit (base) to another in the row of such printing units, a variation in the performance of neighboring printing elements between the arrayed printing units and heat retained in each driving block at the time of recording.
In particular, in the case of an ink-jet printhead, not only a variation in the neighboring printing elements between the arrayed printing units but also a decline in ink fluidity owing to the gaps between printing units results in lower yield in the final stage of the printhead manufacturing process. For this reason, the state of the art is such that these printheads are not readily available on the market in large quantities regardless of the fact these printheads exhibit highly satisfactory capabilities.